ALCOSAN Preliminary Planning Phases I, II, and III

DLZ was the lead drilling firm for the Allegheny County Sanitary Authority (ALCOSAN) Preliminary Planning Team, performing a majority of the borings for each of the 3 Phases. Drilling more than 70 geotechnical borings throughout Allegheny County, to assist in the determination of the potential route and depth for the proposed sanitary relief tunnel, as well as potential other connection areas for ALCOSAN.

Phase I Preliminary Planning

DLZ began Phase I in 2016 and recently completed Phase III in 2020. Each Phase had unique challenges, including aggressive schedules, deep/difficult depths, river borings as well as specialty monitoring and testing.

Phase II Preliminary Planning

During Phase II, ALCOSAN had the intent for DLZ utilizing a minimum of 4 CME Drill Rigs at one time and complete thirty-two deep borings in a few months, including geophysical and infiltration testing. DLZ began the work with multiple rigs, however due to project limitations, the project timeline was extended.

Phase III Preliminary Planning

A majority of the borings were on land, however Phase III did include seven borings on the Ohio, Allegheny and Monongahela Rivers. The river borings were drilled from a barge and using multiple crews working 24 hours a day, 7 days a week, until completed. The land boring locations were spread around the greater Pittsburgh area. In addition to ALCOSAN, multiple entities were involved including the Pittsburgh URA, Parks and Rec’s as well as private property owners. The borings varied in depth, depending on the project needs, from approximately 100 feet to 450 feet below the ground surface and to obtain soil samples from the ground surface to the top of bedrock, and to obtain continuous HQ3 rock core samples from top of bedrock to the specified depths.

After drilling, DLZ representatives organized and stored the rock core samples for laboratory sample preparations and long-term storage. All soil samples were distributed to other team members for laboratory testing, along with the rock core samples for unconfined compression testing. However, Point Load testing of the rock core was performed in DLZ’s Bridgeville, Pennsylvania Laboratory.

DLZ flushed the boreholes and prepared select locations for examination and geophysical testing by a subconsultant. Our field staff monitored and documented the geophysical testing. Afterwhich, DLZ conducted the in-situ infiltration testing (packer testing) in HQ diameter holes using a high precision data logged test unit by RST instruments and inflatable straddle packer system from QSP specially constructed for this project.




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Pittsburgh, Pennsylvania